1. Field of the Invention
The present invention relates to ignition timing control systems for spark ignition internal combustion engines (hereinafter simply referred to as an engine), and more particularly, to such a method in which the spark timing is controlled by feedback related to the presence or absence of knocking.
2. Description of the Prior Art
With known engines, to ensure effective development of the engine torque, it is generally preferable to control the ignition timing in such a manner that it is advanced to a spark angle which produces the maximum torque (i.e., MBT or Minimum Spark Advance for Best Torque). However, it has been known that knocking will occur if the spark ignition timing is advanced excessively and that the critical knock spark advance at which knocking occurs will be less than the MBT depending on the engine conditions. Thus there is a range in which knocking will be caused when the ignition timing is advanced to the MBT. There is another disadvantage that since the critical knock spark advance varies depending on the engine conditions, the octane number of the fuel used and the presence of deposits in the combustion chamber, the actual ignition timing is inevitably advanced to an angle considerably less than the MBT, thus making it impossible to develop a sufficient torque.